The scapula, commonly known as the “shoulder blade”, is a flat, triangular bone that lies over the back of the upper ribs. A right scapula 100 is depicted in posterior, anterior, and right side views in FIGS. 1A, 1B, and 1C, respectively. The posterior surface of the scapula 100 can be readily felt through a patient's skin. The scapula 100 serves as an attachment point for some of the muscles and tendons of the arm, neck, chest, and back, and aids in the movements of the arm and shoulder. The scapula 100 is also well padded with muscle, so that it may be difficult to palpate boney landmarks. The rear surface of each scapula 100 is divided into unequal portions by a spine 102. This spine 102 leads to a head 104, which ends in the acromion process 106. A coracoid process 108 forms a prominence of the shoulder that curves forward and down below the clavicle (collarbone, not shown). The acromion process 106 joins the clavicle and provides attachments for muscles of the arm and chest muscles. The acromion process 106 is a bony prominence at the top of the scapula 100. On the head 104 of the scapula 100, between the acromion and coracoid processes 106 and 108, is a depression or cavity called the glenoid vault 110, shown partially in dashed line in the Figures. The glenoid vault 110 joins with the head of the upper arm bone (humerus, not shown) in a ball-and-socket manner to enable articulation of the shoulder joint thereby formed. Similarly, though not shown, an acetabulum of the hip joins with a head of an upper leg bone (femur) to form an analogous ball-and-socket manner for hip joint articulation.
For treatment of various problems with the shoulder, hip, or other body joint or bone (such as degenerative arthritis and/or traumatic injury), one method of providing relief to a patient is to replace the articulating surfaces with an artificial or prosthetic joint. In the case of a shoulder, the humerus and glenoid vault 110 articulating surfaces are replaced or resurfaced. In the case of a hip, the femur and acetabulum articulating surfaces can be replaced or resurfaced. Both of these examples are of ball-and-socket type joints. Hinge-type joints, such as the knee or elbow, and static/fixed skeletal components, such as the long bones of the arm or leg, as well as interfaces such as those between spinal vertebrae and intervertebral discs, could also be subject to replacement and/or repair by the implantation of artificial or prosthetic components or other fixation devices related to the treatment of fractures, the sequelae of trauma, congenital pathology, or other issues causing a lack of ideal function. For clarity of description, the subject application will be hereafter described as the rehabilitation and/or replacement of a patient's shoulder joint.
In such surgical procedures, pain relief, increased motion, and/or anatomic reconstruction of the joint are goals of the orthopedic surgeon. With multiple variations in human anatomy, prosthetic systems must be carefully designed, chosen, and implanted to accurately replicate the joints that they replace or the bone structures that they aim to change (in any manner).
A shoulder replacement procedure may involve a partial shoulder replacement (not shown) or the total shoulder replacement shown in FIG. 2. In a total shoulder replacement procedure, a humeral component 212 having a head portion is utilized to replace the natural head portion of the upper arm bone, or humerus 214. The humeral component 212 typically has an elongated stem which is utilized to secure the humeral component to the patient's humerus 214, as depicted. In such a total shoulder replacement procedure, the natural bearing surface of the glenoid vault 110 is resurfaced, lined, or otherwise supplemented with a cup-shaped glenoid component 216 that provides a bearing surface for the head portion of the humeral component 212. The depicted total shoulder replacement of FIG. 2 is an “anatomical” shoulder replacement. A “reverse” shoulder replacement is also known in the art.
Standard prosthetic glenoid components 216 are available in a number of different sizes and configurations. However, most are designed for use in an scapula having minimal bone loss or deformity. When the scapula has bone loss and/or significant pathology due to disease or trauma, the standard glenoid component 216 may be difficult to implant and/or may not enable desired shoulder function, if it cannot be implanted in a preferred manner. The surgeon may thus need to substantially modify the patient's glenoid vault 110 during surgery in an attempt to make the standard glenoid component 216 fit into the glenoid vault. Presurgical planning tools are available to help the surgeon anticipate the changes which will be needed to reform the patient's pathological anatomy. However, the surgeon cannot always readily determine whether even a remodeled glenoid vault 110 will fit as desired with a standard prosthesis because the surgeon does not know how a “normal” glenoid vault 110 (for which the standard prosthesis is designed) should be shaped for that patient.
It is known to use computer aided design (“CAD”) software to design custom prostheses based upon imported data obtained from a computerized tomography (“CT”) scan of a patient's body. For example, mirror-imaged CT data of a patient's contralateral “normal” joint could be used, if the contralateral joint does not also display a pathological anatomy. However, using a unique prosthesis design for each patient can result in future biomechanical problems resulting from a non-proven design and takes away the familiarity that the surgeon will likely have with standardized prosthesis designs. Thus, prosthesis designs that are entirely customized are considered sub-optimal solutions and may also be extremely expensive to design and produce.
Further, detailed preoperative planning, using two- or three-dimensional images of the shoulder joint, often assists the surgeon in compensating for the patient's anatomical limitations. During the surgery, for example, an elongated pin may be inserted into the surface of the patient's bone, at a predetermined trajectory and location, to act as a passive landmark or active guiding structure in carrying out the preoperatively planned implantation. This “guide pin” may remain as a portion of the implanted prosthetic joint or may be removed before the surgery is concluded. This type of pin-guided installation is common in any joint replacement procedure—indeed, in any type of surgical procedure in which a surgeon-placed fixed landmark is desirable.
In addition, and again in any type of surgical procedure, modern minimally invasive surgical techniques may dictate that only a small portion of the bone or other tissue surface being operated upon is visible to the surgeon. Depending upon the patient's particular anatomy, the surgeon may not be able to precisely determine the location of the exposed area relative to the remaining, obscured portions of the bone through mere visual observation. For example, in a shoulder surgery, the scapula 100 is mobile along the posterior and lateral chest walls and it therefore may be difficult to define the fixed relationship of the glenoid vault 110 to the body of the scapula 100 (i.e., using the plane of the scapula as a reference to the glenoid vault) and/or the body of the scapula to an external coordinate system in the operating room. These factors, particularly in a minimally invasive surgical procedure, may make it difficult for the surgeon to orient the glenoid vault during surgery. Again, a guide pin may be temporarily or permanently placed into the exposed bone surface to help orient the surgeon and thereby enhance the accuracy and efficiency of the surgical procedure.
One goal of shoulder surgery may be to modify the pathologic bone to correct pathologic position to be within the normal range or the normal position of the patient's native anatomy before the bone loss occurred. During surgery, and particularly minimally invasive procedures, the plane of the scapula may be difficult or impossible to determine by direct visual inspection, resulting in the need for assistive devices or methods to define both the pathologic version present at the time of surgery and the intended correction angle.
It is generally believed that there is a preferred orientation for the glenoid component 216 to provide a full range of motion and to minimize the risk of dislocation. Some example orientations of the glenoid component 216 relative to the glenoid face are about 5° of anteversion to about 15° of retroversion; average version is about 1-2° of retroversion. This broadly replicates the natural angle of the glenoid. However, the specific angular orientation of the glenoid portion, as well as the offset and inclination of the glenoid, varies from patient to patient.
With a view to overcoming these and other disadvantages, some arrangements have been recently suggested in which a three-dimensional intraoperative surgical navigation system is used to render a model of the patient's bone structure. This model is displayed on a computer screen and the user is provided with intraoperative three-dimensional information as to the desired positioning of the instruments and the glenoid component 216 of the prosthetic implant. However, surgical navigation arrangements of this type are not wholly satisfactory since they generally use only a low number of measured landmark points to register the patient's anatomy and to specify the angle of the prosthetic implant component (e.g., a glenoid component 216), which may not provide the desired level of accuracy. Further, the information provided by such systems may be difficult to interpret and may even provide the user with a false sense of security. Moreover, these systems are generally expensive to install and operate and also have high user training costs.
Various proposals for trial prosthetic joint components have been made in an attempt to overcome the problems associated with accurately locating the glenoid component 216 of the prosthetic implant. While these trial systems may help with checking whether the selected position is correct, they are not well-suited to specify the correct position initially, and thus there still is user desire for a system which may assist a user in placement of prosthetic implant component in a prepared native tissue site.
Finally, due to factors such as the high cost of operating room time and the patient detriment sometimes posed by lengthy surgeries, the surgeon or other user may wish to simulate a surgical procedure during preoperative planning, in order to become familiar with the tasks that will be required and possibly reduce the time and/or actions needed to perform the surgery.
In summary, preoperative planning and/or simulation, regardless of the planning tasks undertaken or the nature of the changes to be made to the patient's native tissue, will generally reduce the need for intraoperative imaging in most surgical procedures and should result in decreased operative time and increased positional accuracy, all of which are desirable in striving toward a positive patient outcome.